CRETACEOUS FOSSILS. 79 



lobe, each branch being similarly placed, but not so complex; the 

 lateral branches send off numerous spurs above and below, some 

 of which are again divided. Above these three main branches 

 are three smaller ones on each side, increasing in size from above 

 downwards. Lateral saddle like the dorsal, but a third smaller. 

 Inferior lateral lobe half the size of the superior lateral, with 

 nearly the same pattern. Ventral saddle a little smaller than the 

 lateral. Ventral lobe as long as the dorsal, and differing from 

 the superior lateral only in some small details of the smaller 

 branches. 



Figure 30, two-thirds of natural size. 



After a careful study of these specimens, and comparison with all the forms 

 with similar septa, it seems to me more than probable that they should be asso- 

 ciated with C. (Ancyloceras ?) Remond'd. The reasons are as follows: No part of 

 the septum, of either form, would militate against such a union ; the surface orna- 

 mentations of the two are not more unlike than are often found in the same 

 species ; and, lastly, the two groups of specimens are of just the proper size to fit 

 each other, the smallest of the present specimens having a long diameter of 1.9 

 inch, while the largest of the spiral specimens measures 1.7 inch across. 



The remarkable resemblance between the details of the septa of so many forms, 

 widely distinct in external characters, cannot fail to strike the least acute observer. 

 Here we have Crioceras percostatus, C. latus, C. Duvalii, and C. (Ancyloccras?) Re- 

 mondii, with septa differing from the present form much less than is often ob- 

 served among individuals of the same species; and only differing from Ammo- 

 nites Newberryanus in the number of lobes and saddles ; but without any im- 

 portant variation in the pattern of the dorsal, or next two succeeding lobes and 

 their saddles; and yet it would be preposterous to call them all by the same spe- 

 cific name. It will thus be seen, that while the septum is one of the most 

 important aids in determining the species of Cephalopods, it cannot always be 

 relied on, even so far as to prove that specimens belong to the same genus. At 

 the same time, however, when taken in connection with other characters, it is 

 undoubtedly of great value. 



